The present invention relates to a method of increasing efficiency of heating ventilation, air conditioning and refrigeration (HVAC&R) systems, wherein the compressor operates in a rapidly cycled unloaded mode when reduced system capacity is required. The present invention is directed to noticeably reducing the amount of compression work that is performed at these unloaded conditions when no or little amount of refrigerant is pumped through the compressor.
Refrigerant systems are utilized in many applications, such as air conditioners, heat pumps, refrigeration units, etc. As is known, a refrigerant is compressed in a compressor and then is circulated throughout the refrigerant system to condition a secondary fluid such as air supplied to a climate controlled indoor environment. Most of the time, the refrigerant systems operate unloaded, since full-load capacity is not demanded to compensate for various components of thermal load in the conditioned environment. Therefore, it is desirable to operate the refrigerant system as efficiently as is possible, and especially at part-load conditions.
Improving compressor efficiency is a goal of a design engineer as a compressor typically represents the highest source of power consumption in the refrigerant system. The compressors consume power by compressing the refrigerant from a suction pressure to a discharge pressure. The refrigerant system controls known in the art monitor and maintain temperature and humidity in the conditioned environment within specified tolerance bands, and adjust the capacity provided by the refrigerant system via compressor unloading when the thermal load in the conditioned space and demand for the refrigerant system capacity are reduced.
Various ways of reducing refrigerant system capacity by compressor unloading are known. In one known method, compression elements of a so-called scroll compressor are allowed to move in and out of engagement with each other at a fast periodic rate, typically being in the range of 5 to 30 seconds. When the two compression elements are engaged, the compressor provides a full-load capacity. When the two compression elements are out of engagement, they will no longer compress and circulate the refrigerant throughout the system.
Another way of unloading the compressor is to allow at least a portion of compressed refrigerant return to a suction line.
In either case, a noticeable amount of power is consumed to compress the residual refrigerant inside the compressor. As an example, in the system mentioned above, wherein the scroll compression elements are allowed to move away from each other, there is still some compression taking place on residual refrigerant, resulting into lost compression work and reduced refrigerant system efficiency.
The present invention is directed to reducing the amount of such wasted compression work and improving refrigerant system efficiency at part-load operation.